Stavudine

Description

Stavudine, a dideoxynucleoside analog of thymidine, has been introduced in the U.S.A. for the treatment of late-stage AIDS patients who are refractory to other AIDS treatments. Similar as other currently available agents for AIDS treatment such as zidovudine (AZT), didanosine, and zalcitabine, the anti-HIV activity of these 2'3'- dideoxynucleosides is ascribed to the inhibitory effect of their corresponding 5'- triphosphates against the HlVsncoded RNAdependent DNA polymerase (reverse transcriptase). While some of these drugs have rapid development of drug resistance, stavudine is active against AZT-resistant HIV strains. It has a favorable pharmacokinetic profile with more complete and less variable oral absorption than AZT and didanosine and has a bioavailability of 80-90%.

Chemical Properties

Colourless solid

Originator

Bristol-Myers Squibb (U.S.A.)

Uses

angiotensin 1 receptor antagonist

Uses

Stavudine (Zidovudine EP Impurity A) is used as an antiviral. A reverse transcriptase inhibitor.

Indications

Stavudine (d4T, Zerit) is a thymidine nucleoside analogue that is active against HIV-1 and HIV-2. It is approved for the therapy of HIV infection as part of a multidrug regimen and is also used for postexposure prophylaxis.

Definition

ChEBI: A nucleoside analogue obtained by formal dehydration across positions 2 and 3 of thymidine. An inhibitor of HIV-1 reverse transcriptase

Manufacturing Process

A 3 liter, 3 necked round-bottomed flask was equipped with an overhead stirrer and paddle, a 500 ml dropping funnel and a Claisen adapter containing a drying tube and a thermometer. Thymidine (200 g, 0.82 M) and pyridine (750 ml) were added to the flask. The mixture was stirred and warmed with a water bath (20 min) to give a clear solution. The solution was then cooled in an ice bath to 0°-3°C and the dropping funnel was charged with methanesulfonyl chloride (206.5 g, 1.08 M). The methanesulfonyl chloride was then added dropwise over 40 min with no noticeable exotherm. The solution was stirred at 0°C for 1 h and then stored at 5°C for 18 h. The light brown mixture was then poured onto rapidly stirred water (3 L) containing ice (approx. 500 g). The desired product crystallised immediately. After stirring for 0.5 h, the product was collected by filtration and washed several times with water (3 times 100 ml). The white solid was then dried under vacuum overnight (322 g, 98% yield). The product was recrystallised from hot acetone to give 267 g of the 3',5'-di-O-(methanesulfonyl)thymidine as white solid (81% yield), melting point 169°-171°C (lit. 170°-171°C).
3',5'-Di-O-(methanesulfonyl)thymidine (248 g, 0.62 M) was added in portions to a stirred solution of sodium hydroxide (74.7 g, 1.87 M) in water (1.6 L). On addition the reaction mixture became a yellow-orange solution. This stirred solution was then heated to reflux for 2 h. Once the reaction mixture had cooled to room temperature, 6 N hydrochloric acid (100 ml) was added. The reaction mixture was concentrated in vacuo by removing 1.3 L of water. The resulting slurry was cooled in an ice bath for 2 h. The solid was then filtered and washed sparingly with ice water, and then vacuum dried to constant weight (103.7 g, 74%). The 1-(3,5-anhydro-2-deoxy-β-D-threopentofuranosyl) thymine, melting point 188°-190°C (lit. 190°-193°C) was used without further purification.
2 Methods of preparation of 1-(2,3-dideoxy-β-D-glycero-pent-2- enofuranosyl)thymine
1. To a 3-necked, 1 L round-bottomed flask equipped with a mechanical stirrer, thermometer and nitrogen inlet was added dry DMSO (400 ml) and oxetane (90.0 g, 0.402 M). To this solution was added 97% KOtBu (74 g, 0.643M) in 1.5 g portions over 25 min. The temperature was maintained between 18° and 22°C by means of an external ice bath. After the addition was complete the reaction was stirred for a further 1 h and no further rise in temperature was observed and TLC indicated that the reaction was approximately 90% complete. The reaction was stirred at 21°C for 16 h, after which time TLC indicated that the reaction was complete. The viscous solution was poured onto cold (4°C) toluene (3 L), resulting in a beige colored precipitate. The temperature of the mixture rose to 7°C upon addition of the DMSO solution. The mixture was occasionally swirled over 20 min, then filtered on a 18.5 cm Buchner funnel. The collected yellowish solid was washed twice with cold toluene and allowed to dry under suction for 1 h. The solid was dissolved in 300 ml of water, whereupon two layers formed. The mixture was placed in a separatory funnel and the upper layer (containing residual toluene) was discarded. The aqueous layer was placed in a 1 L beaker equipped with a pH probe, magnetic stirring bar and thermometer. The temperature was cooled to 10°C by the use of an external ice bath. Concentrated HCl was added dropwise to the stirred solution at a rate in which the temperature was kept below 15°C. After the addition of HCl (50.5 ml, 0.61 M) the pH = 70.1 and a precipitate began to form. To this thick mixture was added potassium chloride (70 g) and stirring was continued at 5°C for 1 h. The precipitate was collected and sucked dry for 2 h, then air dried for 16 h. The solid was crushed up and slurried in hot acetone (500 m) and filtered. The residue in the filter paper was rinsed with hot acetone (2 times 200 ml), then slurried again with hot acetone (300 ml), filtered, and washed once more with hot acetone (2 times 100 ml). The combined filtrate was concentrated to dryness to give 51.3 g (57%) of the 1-(2,3-dideoxy-β-Dglycero- pent-2-enofuranosyl)thymine (d4T) as an off-white solid, melting point 165°-166°C.
2. Tetrabutylammonium fluoride (0.22 mL, 0.22 mM, 1.0 M) was added to a suspension of the 1-(3,5-anhydro-2-deoxy-beta;-D-threopentofuranosyl) thymine (25 mg, 0.11 mM) in dry THF (3 ml). The mixture was heated to reflux for 18 h, at which time the reaction appeared to be complete. After cooling, the solvents were removed in vacuo and the residue was dissolved in CH2Cl2/MeOH/NH4OH (90:10:1). Purification was performed on a 20 mm flash chromatography column, eluting with CH2Cl2/MeOH/NH4OH (90:10:1). Concentration of the fractions containing the product afforded 18 mg (72%) of the dideoxy-β-D-glycero-pent-2-enofuranosyl)thymine (d4T).

brand name

Zerit (Bristol-Myers Squibb).

Therapeutic Function

Antiviral

Antimicrobial activity

Stavudine is active against HIV-1, HIV-2 and HTLV-1.

Acquired resistance

Resistance to stavudine is identical to that seen for zidovudine. Mutations at positions 41, 67 and 70, and positions 210, 215 and 219 (the ‘thymidine analog mutations’) of the reverse transcriptase genes are associated with diminished antiretroviral efficacy.

General Description

White crystalline solid or powder. Odorless.

General Description

Stavudine, 2'3'-didehydro-2'-deoxythymidine (D4T, Zerit), isan unsaturated pyrimidine nucleoside that is related to thymidine.The drug inhibits the replication of HIV by a mechanismsimilar to that of its close congener, AZT.Stavudine is bioactivatedby cellular enzymes to a triphosphate.
Stavudine is available as capsules for oral administration.The drug is acid stable and well absorbed (about 90%) followingoral administration. Stavudine has a short half-life(1–2 hours) in plasma and is excreted largely unchanged(85%–90%) in the urine.As with ddC, the primary doselimitingeffect is peripheral neuropathy.
Stavudine isrecommended for the treatment of adults with advancedHIV infection who are intolerant of other approved therapiesor who have experienced clinical or immunological deteriorationwhile receiving these therapies.

Air & Water Reactions

Water soluble.

Reactivity Profile

Stavudine is sensitive to heat. Incompatible with strong oxidizing agents .

Hazard

Moderately toxic by ingestion.

Fire Hazard

Literature sources indicate that Stavudine is combustible.

Pharmaceutical Applications

An analog of thymidine formulated for oral administration.

Biochem/physiol Actions

2′,3′-Didehydro-3′-deoxythymidine is a nucleoside analog, which inhibits HIV replication?in vitro. Stavudine has the ability to enter the cells by non-facilitated diffusion. It possesses inhibitory activity against moloney murine leukemia virus, friend murine leukemia virus and simian immunodeficiency virus.

Pharmacokinetics

Oral absorption: 86%
C_max 40 mg twice daily: 0.54 mg/L
Plasma half-life: 1.4 h
Volume of distribution: 0.66 L/kg
Plasma protein binding: <5%
Absorption and distribution
It is rapidly absorbed with or without food. CNS penetration is moderate. The estimated semen:plasma ratio is >1. It is secreted into breast milk.
Metabolism and excretion
The metabolic fate in humans has not been elucidated. Renal elimination accounts for approximately 40% of overall clearance at a rate almost twice that of endogenous creatinine, indicating glomerular filtration and active tubular secretion. Clearance decreases as creatinine clearance decreases and the dosage should be adjusted in patients with reduced renal function. Pharmacokinetics are not significantly altered in patients with hepatic impairment.

Clinical Use

Treatment of HIV infection in adults and children

Side effects

The adverse effects with which stavudine is most frequently associated are headache, diarrhea, skin rash, nausea, vomiting, insomnia, anorexia, myalgia, and weakness. Peripheral neuropathy consisting of numbness, tingling, or pain in the hands or feet is also common with higher doses of the drug. Significant elevation of hepatic enzymes may be seen in approximately 10 to 15% of patients. Lactic acidosis occurs more frequently with stavudine than with other NRTIs. Viral resistance to stavudine may develop, and cross-resistance to zidovudine and didanosine may occur.

Side effects

Toxicity includes peripheral neuropathy, lactic acidosis, hepatomegaly with steatosis and liver failure, lipoatrophy and pancreatitis. Combination therapy with didanosine results in higher frequency of these toxicities, and fatalities have been reported in pregnant women. The use of the two drugs in combination is no longer recommended. It competes with zidovudine for the same intracellular phosphorylating enzymes and co-administration is contraindicated.

Drug interactions

Potentially hazardous interactions with other drugs
Antivirals: zidovudine may inhibit intracellular activation - avoid; increased risk of side effects with didanosine - avoid; increased risk of toxicity with ribavirin.
Cytotoxics: effects possibly inhibited by doxorubicin; increased risk of toxicity with hydroxycarbamide - avoid.
Orlistat: absorption of stavudine possibly reduced

Metabolism

Stavudine is metabolised intracellularly to the active antiviral triphosphate. Following an oral 80-mg dose of [14C]-stavudine to healthy subjects, approximately 95% and 3% of the total radioactivity was recovered in urine and faeces, respectively. Approximately 70% of the orally administered stavudine dose was excreted as unchanged drug in urine. However, in HIV-infected patients, 42% (range: 13-87%) of the dose is excreted unchanged in the urine, by active tubular secretion and glomerular filtration.

Precautions

Stavudine possesses several clinically significant interactionswith other drugs. Although hydroxyurea enhancesthe antiviral activity of stavudine and didanosine,combination therapy that includes stavudine anddidanosine, with or without hydroxyurea, increases therisk of pancreatitis. Combinations of stavudine and didanosineshould not be given to pregnant women becauseof the increased risk of metabolic acidosis.Zidovudine inhibits the phosphorylation of stavudine;thus, this combination should be avoided.

References

1. routledge c, bromidge sm, moss sf et al. characterization of sb-271046: a potent, selective and orally active 5-ht (6) receptor antagonist. br j pharmacol. 2000 aug; 130(7):1606-12.2. marcos b, chuang tt, gil-bea fj, ramirez mj. effects of 5-ht6 receptor antagonism and cholinesterase inhibition in models of cognitive impairment in the rat. br j pharmacol. 2008 oct;155(3):434-40.